Fuel injection pump



NOV. 11, 1969 H, STAUDT FUEL INJECTION PUMP Filed May 13, 1968 a ./V n 1 B B Y 1/ .7 IY'PII bkffll w m \1 his ATTORN 3,477,386 FUEL INJECTION PUMP Heinrich Staudt, Markgroningen-Talhausen, Germany, as-

signor to Robert Bosch G.m.b.H., Stuttgart, Germany, a corporation of Germany Filed May 13, 1968, Ser. No. 728,516 Claims priority, application Germany, June 16, 1967,

Int. Cl. F04!) 19/22, 7/06; F02m 55/00 US. Cl. 103-154 4 Claims ABSTRACT OF THE DISCLOSURE A fuel injection pump of the type including a piston reciprocating in a bore, means for controlling the backfiow of fuel to meter the fuel quantities to be delivered to an engine; the improvement resides in the provision on said piston of two axially spaced circumferential annular grooves interconnected by a helically extending groove; said circumferential annular grooves are so arranged that during a portion of the pressure stroke of said piston said 'backfiow fuel is forced into said grooves and at the end of the suction stroke of said piston the fuel confined in said grooves is discharged therefrom thus effecting a thorough lubrication of the sliding faces, a continuous exchange of fuel and an efficient removal of solid particles from between the sliding faces.

BACKGROUND OF THE INVENTION; PRIOR ART The invention relates to fuel injection pumps of the type having backflow control means for varying the delivered fuel quantities, a reciprocating pump piston executing strokes of constant length, and a cylindrical bore in which said piston reciprocates. The wall of said bore is provided with an annular discharge groove. Such an assembly is described, for example, in Swiss Patent No. 143,812.

Fuel injection pumps of the type outlined above which deliver heavy fuel oil of high viscosity at peak pressures of 1,000 kg./cm. or more, are exposed to the danger of scoring. It is known that the development of fuel injection pumps has lead to increasing peak pressure values. This is closely coupled with the overall development of internal combustion engines for continuously increasing effective pressures and rotational speeds to arrive at increased exploitations of efiiciency. Furthermore, high viscosity heavy oils, the use of which is required for economic reasons, contain solid foreign materials and finely dispersed or dissolved organically bound metals such as vanadium, sodium and nickel. While the solid foreign materials are substantially eliminated by means of careful filtering, the dissolved and dispersed metal compounds remain in the heavy oil and are, in conjunction with the high peak pressure values, the principal cause for the scoring of the pistons. Therefore, all sliding surfaces of the piston have to be well lubricated, the aged or waste fuel wedged between the piston and thestationary guiding faces continuously exchanged and the residues removed so that, by eliminating scoring, the wear of the sliding faces of the piston remains within required tolerances.

It is known to enlarge the clearance of the pistons and to provide pistons of conical shape in an attempt to eliminate scoring. Such measures may be taken, however, only on a limited scale and, furthermore, in the case of the delivery of heavy oils, have not yielded satisfactory results.

It is further known to use fuel injection pumps having pistons provided with one or more annular grooves to store, for lubricating purposes, the fuel which leaks be- United States Patent 3,477,386 Patented Nov. 11, 1969 tween the piston and the cylindrical bore in which it reciprocates. These grooves are also intended to serve as dirt catchers and dirt collectors in order to keep away dangerous particles from the narrow clearance between the piston and the stationary guide face of the bore. In US. patent to Bremser, No. 2,420,164, there is described a pump of the aforenoted type, the piston of which comprises a discharge groove which in certain positions of the piston communicates with the suction chamber. The piston further comprises one or more annular collecting grooves for the leaking fuel arranged adjacent the pump driving means. Such an arrangement is purported to provide for a uniform lubrication of the piston.

It is a disadvantage of the aforenoted solutions that the residues are stored and concentrated in the grooves of the piston. Further, the lubrication of the sliding piston faces adjacent the driving means is insufficient because of the restriction in the clearance between the piston and the guide bore. Examinations of the residues in the grooves proved that the material is overwhelmingly waste oil, that is, aged fuel which is no longer capable of lubrication. This indicates that a controlled exchange of fresh oil for used oil has not been taking place.

Also, in the grooves which are connected with the suction conduit through a narrow and long channel such as disclosed in the aforenoted Swiss Patent No. 143,812, harmful materials accumulate which cause, after a shorter or longer period of operation, a scoring of the piston due to the larger particles that grow by the build-up of the smaller residues.

Pumps are further known wherein the sliding faces of the piston are lubricated with the fuel 'as described in German published patent application No. 1,022,907 or with lubricating oil as described in German Patent No. 513,156. An embodiment of the fuel injection pump disclosed in the last-named patent includes a lock for leaking oil in which an obliquely disposed groove extends from a piston groove filled with oil supplied by the lubricating circuit of the engine. The provision of additional lubricating conduits and control members for the metering of the lubricating material involves substantial expenses and is further not favored because of its tendency to malfunction. Furthermore, such a lubrication of fuel injection pumps of the type under consideration has not proved to be sufiiciently effective.

OBJECT AND SUMMARY OF THE INVENTION It is an object-of the invention to provide a fuel injection pump in which the pistons are sufficiently and uniformly lubricated in a simple manner and an accumulation of harmful materials is avoided so that a continuous, loadstable and r.p.m.-stable operation of the fuel injection pump (particularly for medium and large diesel engines) is ensured with a delivery of fuel (particularly heavy oils) at pressures up to 1,000 kg./cm. or more.

Briefly stated, according to the invention the side face of the piston is provided with at least one, preferably two, helically extending grooves which establish communication between an annular, circumferential fuel collecting groove provided in the face of the piston adjacent the driven end and an annular, circumferential fuel collecting groove provided in the face of the piston remote from its driven end; at the end of the delivery stroke the last-named groove registers with a discharge groove disposed circumferentially in the bore in which the piston reciprocates. By virtue of the aforenoted structure an excess pressure builds up down to the groove at the driven end of the piston.

The invention will be better understood as well as further objects and advantages will become more apparent from the ensuing detailed specification of two exemplary embodiments taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary axial view of one embodiment of the novel fuel injection pump; and

FIG. 2 is a fragmentary axial view of another embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to FIG. 1, in the housing 1 of a partially shown fuel injection pump there is mounted a guide sleeve 2 in the bore of which reciprocates a pump piston 3. The guide sleeve 2 is closed off at its upper end by means of a pressure valve housing 4 having a movable valve member 5. A pump work chamber 6 is connected with a suction chamber 8 through inlet ports 7. Facing the mouth of each inlet port 7 is a bafile bolt 9 secured to housing 1.

The bore of the guide sleeve 2 is provided with a circumferential annular discharge groove 10 which is connected to the funnel-shaped mouth 7a of one of the inlet ports 7 by means of channel 11 and thus communicates with the suction chamber 8.

The piston 3 is provided, in addition to a recess 12 open towards the pump work chamber 6, with two circum ferential, annular fuel collecting grooves 13 and 14 which are interconnected by means of a helically extending groove 15. Groove 14 is at the driven side of the piston 3 (the driving means are not shown), while groove 13 3 is disposed remotely therefrom. Although only a single connecting groove 15 is shown in the drawing, two or more parallel or oppositely extending helical grooves may be used. In FIG. 1 the piston 3 is shown at the end of its suction stroke; as seen, in this position of piston 3 the groove 14 projects beyond the lower end of the piston guide sleeve 2.

The fuel collecting groove 13 is so disposed and its width so dimensioned that it registers with the discharge groove 10 during the pressure stroke of the piston from shortly before the earliest possible beginning of the backflow stroke until the termination thereof. The backflow stroke is that part of the pressure stroke of the piston, during which no fuel delivery to the engine takes place.

The earliest possible beginning of the backflow stroke occurs under light load conditions when the smallest quantities of fuel are delivered to the engine. In such a case the downwardly disposed oblique control edge 12:: of a fuel injection pump registers with the inlet port 7 after a small effective delivery stroke. In pumps having upwardly disposed oblique control edges, the backflow stroke is of constant magnitude.

OPERATION OF THE PREFERRED EMBODIMENT If the pump is set into motion from its position shown in FIG. 1, the piston 3 moves during its pressure or delivery stroke, in the direction of the pump work chamber 6. As a result, the fuel collecting groove 14 enters into the guide sleeve 2; the inlet ports 7 are closed by the upper terminal portion of the piston 3 and the fuel is delivered to the engine through the opened valve member until the recess 12 opens towards the pump work chamber 6 arrives into registry with the inlet port 7. At that moment the highly pressurized fuel is expelled into the suction chamber 8. The fuel jet, broken by bafile bolts 9, causes a turbulent motion of the fuel present in the suction cham ber 8 and further causes an increase in its pressure.

Since, during the registry between the recess 12 and the inlet ports 7, the discharge groove communicating with the suction chamber 8 is in registry with the annular groove 13, a pressure build-up also occurs in the latter as well as in the helical groove and in the annular groove 14. Also, fresh fuel is forced into the groove 13. The excess pressure prevails in grooves 13 and 14 until the groove 14 emerges, at the end of the suction stroke of the piston, from the piston guide sleeve 2. i

As the groove 14 clears the sleeve 2, a decompressio results which causes the harmful residues and the fuel no longer capable of lubrication to be expelled from the groove 14. The expelled fuel clinging to the piston below the groove 14 is wiped off by the terminal edge of sleeve 2 during the subsequent delivery stroke of the piston. This effect is aided by gravity acting on the residues of high specific weight and by their inertia effective both at the end of the suction stroke (negative acceleration) and at the beginning of the delivery stroke (positive acceleration) of the piston.

In addition to a uniform lubrication of the entire piston, there is also achieved an efficient rinsing and cleaning of the discharge groove 10 and the fuel collecting grooves 13 and 14.

DESCRIPTION OF A MODIFIED EMBODIMENT Turning now to FIG. 2, the embodiment depicted therein differs from the previously-discussed embodiment only in the arrangement of the fuel collecting groove 14 and the pitch of the helical groove 15. The groove 14 is so arranged that it always remains inside the pump guidesleeve 2.

A fuel injection pump constructed in accordance with FIG. 2 is particularly advantageous when fuel having a high degree of purity and good lubricating properties is delivered under pressure conditions which are lower than those which the precedingly described embodiment operates. In view of these conditions, a projection of groove 14 beyond the sleeve 2 and thus a periodic discharge of the fuel confined in grooves 13, 14, 15 is not necessary; the system of helically interconnected grooves results in a very efficient and uniform lubrication, particularly of the piston faces adjacent the driven end of the piston.

Although only two embodiments of the invention have been depicted and described, it will be apparent that these embodiments are illustrative in nature and that a number of modifications in the apparatus and variations in its end use may be effected without departing from the spirit or scope of the invention as defined in the appended claims.

That which is claimed is:

1. In a fuel injection pump of the type including a reciprocating piston having a driven end and executing alternating suction strokes and pressure strokes in a cylindrical bore, one part of each pressure stroke constituting a delivery stroke during which fuel is injected into an engine with which said pump is associated, the other part of each pressure stroke constituting a backflow stroke during which fuel is forced by said piston into a suction chamber of said pump, a circumferential annular discharge groove formed in said bore and being in communication with said suction chamber, the improvement comprising,

(A) a first annular circumferential groove formed in the cylindrical wall of said piston remote from the driven end thereof, said first annular circumferential groove adapted to register with said discharge groove during one portion of the pressure stroke of said piston, said portion extending to the end of the pressure stroke,

(B) a second annular circumferential groove formed in the cylindrical wall of said piston adjacent the driven end thereof, and

(C) at least one helically extending connecting groove formed in the cylindrical wall of said piston and effecting communication between said first and said second annular circumferential grooves,

2. A fuel injection pump as defined in claim 1, wherein said second annular circumferential groove is adapted to at least partially clear said cylindrical bore at the end of each suction stroke of said piston.

3. A fuel injection pump as defined in claim 1, wherein said second annular circumferential groove is adapted to remain inside said cylindrical bore at all times during the reciprocation of said piston.

6 4. A fuel injection pump as defined in claim 1, wherein 1,866,217 7/1932 Mayer 103--157 the width of said first annular circumferential groove is 1,944,919 l/1934 Bischof 103-154 dimensioned so that it is adapted to register with said 2,291,601 8/1942 Bancroft 103-157 discharge groove shortly prior to the earliest possible be- 2,612,842 10/1952 Steven et a1. 103--41 ginning of said backflow stroke. 5 2,745,350 5/ 1956 Capsek 10341 2,278,395 3/1942 Lichte et a1. 103154 References Cited UNITED STATES PATENTS 1,369,666 2/1921 Johnson 103 154 US. Cl. X.R. 1,546,596 7/1925 Mader 103-154 10 103-157 HENRY F. RADVAZO, Primary Examiner 

